电子束与复合靶作用后辐射特性的数值模拟

建立了复合靶的蒙特卡罗粒子输运计算模型，以“闪光二号”加速器为电子束源，模拟了电子和光子在不同材料中的输运规律，研究了钽和聚乙烯组成的复合阳极靶对辐射X射线场的影响。模拟结果表明：随着钽厚度的增加，辐射X射线平均能量增大，能量转换效率先增大后减小；聚乙烯可明显减小辐射场中的电子份额。当钽和聚乙烯的厚度分别取20 μm、3 mm时，辐射场中平均光子能量为102.68 keV；光子总能量为88.62 J，远大于电子总能量0.02 J；X射线能量转换效率为0.57%。根据数值模拟结果和实验条件设计了复合靶，计算和测得的X射线平均能量分别为108和121 keV，二者符合得较好。

Numerical Simulation on Radiation Characteristic of Composite Target

Electrons energy distribution of Flash Ⅱ accelerator was calculated using current and voltage. The Monte Carlo N particle transport code was used for the radiation simulation, and the influence of target thickness and structure on X-ray parameters was simulated. The numerical results indicate that the average energy of photons increases with tantalum target thickness, and the conversion efficiency of X-ray has a maximum value. The ratio of total energy of photons to forward electrons distinctly decreases when polythene materials are added behind tantalum target. As an example, for 20 μm tantalum and 3 mm polythene targets, the average energy of photons is 102.68 keV, X-ray energy is 88.62 J which is greater than 0.02 J of the forward electrons energy, and the conversion efficiency is 0.57%. One composite target was designed for Flash-Ⅱ accelerator based on the simulation results and engineering conditions, and the simulation results agree well with the measured data.